In saucepan, bring blueberries, sugar and orange juice to boil; reduce heat and simmer until tender, about 10 minutes.Whisk in cornstarch and boil, stirring, until thickened, about 1 minute. Pour into a bowl. Place plastic wrap directly on surface. Refrigerate until cooled and bearing a consistency similar to that of a jam, about 1 hour or up to 1 day before using.In a large bowl, stir together oats, flour, brown sugar, salt and baking soda. Add butter to form a crumbly mixture.Reserve 1 1/2 cups of crumbs; pat remaining dough evenly into the bottom of a greased 9 x 13 inch pan. Spread blueberry mixture over the base. Crumble reserved amount of the base/topping over the blueberry mixture.Bake at 350F until light golden, about 40-45 minutes. Let cool completely on rack before cutting. Store in refrigerator.